1. Field of the Invention
The present invention relates to a brush holding device of a DC motor.
2. Description of Related Art
A DC motor having a brush is provided with a brush holding device as described in, for example, in Japanese Patent No. 3486094. As shown in FIG. 7, this brush holding device is constituted by a brush holder 100 made of resin for housing a brush (not shown), and a holder plate 110 to which the brush holder 100 is fixed. The holder plate 110 has a pair of engaging pieces 111 which are partially cut out from the surface thereof, and are bent so as to oppose to each other. The brush holder 100 is provided with, at a bottom part thereof, plate-like convex parts 101 projecting laterally. These plate-like convex parts 101 become caught in the gaps between the engaging pieces 111 and the surface of the holder plate 110.
The above described brush holding device has a problem in that it is difficult for the engaging pieces 111 have a sufficient height, because they are formed by partially cutting out the surface of the holder plate 110. Accordingly, since the gap height between the surface of the holder plate 110 and the engaging piece 111 cannot be made large enough, the plate-like convex parts 101 cannot have a sufficient thickness. This makes it difficult for the brush holding device 100 to have a sufficiently high strength.
In addition, since the brush holder 100 is fitted to the holder plate 110 by inserting the plate-like convex parts 101 into the gaps between the engaging pieces 111 and the surface of the holder plate 110, the brush holder 100 cannot be fixed solidly if the bending strength of the engaging pieces 111 is not high enough. The bending strength of the engaging piece 111 can be increased by increasing its thickness. However, since the thickness of the engaging piece 111 is equal to the thickness of the holder plate 110, it is not possible to make the thickness of the engaging piece 111 larger than that of the holder plate 110. Since increasing the thickness of the holder plate 110 leads to increasing the weight and axial length of a DC motor, it is difficult to increase the thickness of the holder plate 110, especially in a case of a starter motor which is strongly required to be of small size, and light weight.